For the first time the vertical integration of high-silica content low-los channel waveguides on an Si substrate is reported. The fabrication process, which has made the vertical integration feasible, consists of a practical multistep combination of flame hydrolysis deposition (FHD), photolithographic patterning and reactive ion etching. The succesful application to a double integration of singlemode waveguides at 1.55 μm is also reported. This result, which has been possible thanks to the FHD pecularities, by extending the optical interaction to a third dimension, open a wide range of original and promising applications, such as vertically coupled devices or parallel optical signal processors, and it effectively increases the density of optical guided-wave functions available on the substrate.